Methods and apparatus to calculate a distance from a borehole to a boundary of an anisotropic subterranean rock layer

ABSTRACT

Methods and apparatus to calculate a distance from a borehole to a boundary of an anisotropic subterranean rock layer are disclosed. A disclosed example method includes transmitting a first signal from a first transmitter at a first location in a borehole traversing a subterranean formation, receiving the first signal at a first receiver after a first time period at a second location in the borehole, receiving the first signal at a second receiver after a second time period at a third location in the borehole, and calculating a first distance from the first transmitter to a first portion of a boundary of a subterranean rock layer adjacent to the borehole by compensating for an anisotropy of the subterranean rock layer based on the first time period and the second time period.

FIELD OF THE DISCLOSURE

This disclosure relates generally to oil production and, moreparticularly, to methods and apparatus to calculate a distance from aborehole to a boundary of an anisotropic subterranean rock layer.

BACKGROUND

Oil and gas producers typically image subterranean rock layers todetermine the location and shape of the subterranean rock layers. Suchimaging may also be used to identify a boundary between the subterraneanrock layer and an adjacent subterranean rock layer. The imaging is oftenperformed using an imaging tool disposed within a borehole drilled intothe subterranean rock layer to be imaged.

Identifying a boundary of a subterranean rock layer is an importantaspect of oil or gas well production. For example, identifying such aboundary of a rock layer enables oil or gas producers to plan welllocations to efficiently and optimally extract oil or gas. Additionally,knowing the boundary of a rock layer may prevent oil and gas producersfrom drilling into undesired rock layers.

Currently, subterranean rock layer boundaries are imaged and/or measuredby time-indexed waveforms or signals that are emitted by a transmitterand received by sensors or receivers. These receivers are located adistance away from the transmitter in a borehole. Typically, thetransmitter(s) may be located on the surface while the receivers arelocated in a borehole. The signal emitted from the transmitter(s)propagates through the rock layer being logged, reflects and/or refractsoff of a boundary of the rock layer, and is received by the receivers.The waveforms or signals received by the receivers may be processedusing signal migration to determine the distance between the receiversin the borehole and the rock layer boundary. However, the velocity ofthe waveforms or signals may be affected by anisotropic properties inthe logged rock layer or boundary such as faults in the rock layer,cracks in the rock layer, a change in lithology in the rock layer or achange in an unconformity within the rock layer.

SUMMARY

Example methods and apparatus to calculate a distance from a borehole toa boundary of an anisotropic subterranean rock layer are described. Anexample method includes transmitting a first signal from a firsttransmitter at a first location in a borehole traversing a subterraneanformation, receiving the first signal at a first receiver after a firsttime period at a second location in the borehole, and receiving thefirst signal at a second receiver after a second time period at a thirdlocation in the borehole. Additionally, the example method includescalculating a first distance from the first transmitter to a firstportion of a boundary of a subterranean rock layer adjacent to theborehole by compensating for an anisotropy of the subterranean rocklayer based on the first time period and the second time period.

An example apparatus includes a transmitter at a first location totransmit a first signal within a borehole of a subterranean rock layer,a first receiver at a second location in the borehole to receive thefirst signal after a first time period, and a second receiver at a thirdlocation in the borehole to receive the first signal after a second timeperiod. The example apparatus further includes a formation processor tocalculate a first distance from the first transmitter to a first portionof the boundary of the subterranean rock layer by compensating for ananisotropy of the subterranean rock layer based on the first time periodand the second time period.

Alternatively, the example apparatus includes a formation processor tocalculate a first distance from a first transmitter to a first portionof the boundary of a subterranean rock layer by compensating for ananisotropy of the subterranean rock layer based on a first time periodand a second time period corresponding to a first signal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1D show typical seismic-while-drilling tools with one or moretransmitters located at the surface.

FIG. 2 shows a graph representing the effect of anisotropy within asubterranean rock layer.

FIG. 3 shows an example wellsite system including a transmitter andreceivers to implement the example methods and apparatus describedherein.

FIG. 4 shows an example sonic logging-while-drilling tool.

FIG. 5 shows an example seismic imaging tool within a subterranean rocklayer.

FIG. 6 shows the seismic imaging tool transmitting and receiving signalsaffected by anisotropy within the subterranean rock layer of FIG. 5.

FIG. 7 shows an example functional block diagram of the logging andcontrol processor of FIG. 3.

FIGS. 8, 9 and 10 are flowcharts of example processes that may be usedto implement the example logging and control processor, thetransmitters, the receivers, the example formation processor, theexample boundary migrator, command processor, and/or the transmissionmanager of FIGS. 3, 5, 6, and 7.

FIG. 11 is a block diagram of an example processor system that may beused to implement the example methods and apparatus described herein.

DETAILED DESCRIPTION

Certain examples are shown in the above-identified figures and describedin detail below. In describing these examples, like or identicalreference numbers are used to identify common or similar elements. Thefigures are not necessarily to scale and certain features and certainviews of the figures may be shown exaggerated in scale or in schematicfor clarity and/or conciseness. Although the following discloses examplesystems including, among other components, software or firmware executedon hardware, it should be noted that such systems are merelyillustrative and should not be considered as limiting. For example; itis contemplated that any form of logic may be used to implement thesystems or subsystems disclosed herein. Logic may include, for example,implementations that are made exclusively in dedicated hardware (e.g.,circuits, transistors, logic gates, hard-coded processors, programmablearray logic (PAL), application-specific integrated circuits (ASICs),etc.) exclusively in software, exclusively in firmware, or somecombination of hardware, firmware, and/or software. Accordingly, whilethe following describes example systems, persons of ordinary skill inthe art will readily appreciate that the examples are not the only wayto implement such systems. Further, the examples may be implemented byacoustic signals that may include seismic signals, sonic signals,ultrasonic signals and/or any other shear and/or compression signals.

Currently, oil and/or gas producers use time-indexed waveforms of asignal to image a boundary of a subterranean rock layer adjacent to awellbore or a borehole. The frequency, amplitude, and/or energy of thesignal are specified so that the signal can propagate through the rocklayer being logged but reflect off a boundary of the rock layer. Forexample, a signal having a frequency of 8000 Hertz (Hz) may be specifiedto enable the signal to propagate through a first rock layer. However, asignal at this frequency may reflect off a boundary of the rock layer.The boundary may include a change in rock type from the subterraneanrock layer being logged to a second type of rock in a secondsubterranean rock layer, a change in a lithology of the subterraneanrock layer, a change in a fault of the subterranean rock layer, or achange in an unconformity within the subterranean rock layer.

The boundary is imaged by transmitting one or more acoustic signals froma transmitter and recording when the signals are received by one or morereceivers. Each receiver may include one or more sensorscircumferentially located around the receiver so that each sensor maydetect the transmitted signal from a specified direction. The sensorsmay include any type of transducer to convert a detected acoustic (e.g.,seismic, sonic, ultrasonic, etc.) signal into an electrical signaland/or impulse decipherable by a microcontroller, a transistor, and/or aprocessor. By aligning the sensors in specified directions, oil and/orgas producers can determine the direction from which a signal wasreflected. Typically, one or more transmitters) are located at thesurface in proximity of a well site while receivers are included withina tool that is placed within a wellbore or borehole of a rock layerbring logged.

In examples where one or more receivers are included within a toollocated in a borehole, the location of the receivers within the tool maybe fixed. In the case where the receiver locations are fixed, thedistance between each transmitter on the surface and each receiver isknown. In addition to knowing the distances between transmitter(s) andreceivers, oil and gas producers can determine the time for a signal topropagate from a transmitter to each receiver based on a logging andcontrol processor that measures the time period between the signal beingtransmitted and the time at which each receiver receives the signal.

FIGS. 1A-1D show typical seismic-while-drilling tools that include oneor more transmitters 1 at the surface and one or more receivers 2 in aborehole 3. FIGS. 1A and 1B show that the downhole tool may include asingle receiver 2 in the borehole 3. Additionally, FIGS. 1A and 1C showthat a single transmitter 1 may be implemented as a single seismic(e.g., signal) source, while FIGS. 1B and 1D show a plurality of thetransmitters 1 providing respective seismic sources. FIG. 1B shows thereceiver 2 receiving reflections and direct signals from thetransmitters 1, while FIGS. 1C and 1D show multiple receivers 2receiving signals directly from the one or more transmitters 1.

Seismic images may be generated from the arrangements of thetransmitter(s) 1 and the receiver(s) 2 of FIGS. 1A-1D. FIG. 1A shows areflection of the signal off a rock layer boundary or bed boundary 4.The seismic imaging of the bed boundary generates a ‘zero-offset’vertical seismic profile arrangement. FIG. 1B shows a reflection of thesignals off the bed boundary 4. This seismic imaging generates a‘walkway’ vertical seismic profile arrangement. FIG. 1C shows arefraction through salt dome boundaries. This seismic imaging generatesa ‘salt proximity’ vertical seismic profile. FIG. 1D includes signalreflections off the rock layer boundary 4 and/or some direct signalsfrom the transmitter 1. This seismic imaging generates a ‘walk above’vertical seismic profile. The vertical profiles and/or arrangementsreferred to in FIGS. 1A-1D are labeled vertical because the receiver(s)2 are oriented vertically along the borehole 3.

Furthermore, each receiver(s) 2 may include sensors evenly spaced aroundthe circumference of the receiver. To determine the distance from thetool in the borehole 3 to a first portion of the boundary 4 of a rocklayer, the transmitter(s) 1 transmits a first signal. This first signalpropagates in all directions through the rock layer. When the signalreaches the boundary 4 of the rock layer, the signal reflects back tothe borehole 3. The receiver(s) 2 may then detect the reflected signal.Similarly, a second signal may be transmitted by the transmitters) 1 andreceived by the receiver(s) 2 after reflecting off the boundary 4. Thedistance to the boundary 4 can be related to the time for the firstsignal to reach each receiver 2, the distance from each of thereceiver(s) 2 to the transmitter 1, and the velocity of the firstsignal. There may be a separate time-distance relationship for eachsensor within the receiver 2 that receives the reflected first signal.Similarly, the time for the second signal to reach each of the receivers2, the distance from the receivers 2 to the transmitters) 1, and thevelocity of the signal can be related to the distance to the boundary 4.These relationships may then be combined into a semblance model tocalculate the distance to a portion of the boundary 4.

In other typical examples, a sonic tool may be located within theborehole 3. However, in these cases, the signal velocity determined fromthe velocity of the signal in the direction (i.e., parallel to thelongitudinal axis) of the borehole 3 (e.g., the inline velocity) maydiffer from the velocity of the signal propagating through the rockformation. The velocity of the signal may differ in this manner due toanisotropy in the rock layer. For example, an inline signal may have avelocity that differs by 20% compared to a signal traveling in adirection perpendicular or orthogonal to the borehole due to anisotropyin the rock layer. More generally, the signal velocity may differ orvary based on an angle of signal propagation, which may range from adirection along (i.e., parallel to) the longitudinal axis of theborehole to a direction perpendicular to the longitudinal axis of theborehole. For example, if the anisotropy is uniform in the rock layer, asignal traveling at an angle of 22 degrees from the longitudinal axis ofthe borehole may have a velocity that is 5% slower than a signaltraveling in the inline direction (i.e., along the longitudinal axis) ofthe borehole.

FIG. 2 shows a graph defining an example of anisotropy within asubterranean rock layer. The x-axis shows a normalized inline signalvelocity (V_(INL)) and the y-axis shows a normalized orthogonal and/orperpendicular signal velocity (V_(ORT)). The inline signal velocitycorresponds to a velocity of the signal in the formation along an axisparallel to a borehole, where the signal is sent from a transmitterdirectly to a receiver. An anisotropy velocity line 5 shows a velocityof a signal based on an angle of propagation (e.g., θ). The angle ofpropagation is an angle at which a signal propagates through a rocklayer. If the signal is reflected back to the receivers by a boundary ofa rock layer that is parallel to the wellbore, Snell's Law of Reflectionindicates that the angle at which the signal travels when transmitted bya transmitter, the angle at which the signal is reflected off of theboundary of a rock layer, and the angle at which the signal is receivedat a receiver are substantially the same angle. Thus, a signalpropagating through a uniform rock layer should have a constantanisotropic velocity based on the angle of transmission and reception,which is also equal to the angle of propagation for a reflector parallelto the wellbore.

As a result of anisotropy, a signal propagating in the inline directionmay have a normalized signal velocity of 0.8 while a signal propagatingin the orthogonal direction may have a normalized signal velocity of0.9. Thus, in this example, the signal propagating in the orthogonaldirection is 12.5% faster than the signal propagating in the inlinedirection. The example in FIG. 2 shows a signal 6 having an angle ofpropagation θ. Based on the anisotropy velocity line 5, the signal 6propagating through a rock formation at an angle of θ may have anormalized anisotropic velocity of 0.86 (e.g., the length of the vectorrepresenting the signal 6 from the origin to the velocity line 5).

FIG. 2 shows the anisotropy velocity line 5 as approximately linearlydependent on the angle of propagation (e.g., 0.8 in the V_(INL)direction to 0.9 in the V_(ORT) direction). However, in other examples,anisotropy may be exponentially dependent, logarithmically dependent,Gaussian dependent, inversely dependent, and/or may exhibit any othertypes of functional dependence on the angle of propagation. In yet otherexamples, the anisotropy may not depend on the angle of propagation.However, the example methods and apparatus described herein compensatefor any type of anisotropy that varies based on the angle ofpropagation.

As noted above, anisotropy may result from faults in a rock layer,cracks in a rock layer, a change in lithology in a rock layer, and/or achange in an unconformity within a rock layer. Not compensating foranisotropy within a rock layer may create errors in determining adistance of a rock layer boundary from a sonic and/or seismic imagingtool. The error may result from assuming that the signal velocity isuniform in all directions. In practice, when a rock layer is affected byanisotropy, the signal velocity may differ significantly from the inlinesignal velocity based on the angle of propagation. Furthermore, becausethe angle of propagation of the signal received by each receiver and/orsensor is different for each receiver, the signal velocities may bedifferent based on these different angles. As a result of the differencebetween the inline signal velocity and the anisotropic signal velocity,the calculated distance to the boundary may be significantly differentfrom the actual distance.

The difference between the calculated distance and the actual distancemay result in oil or gas producers drilling wellbores or boreholes inrock layers that may not contain the desired natural resources,improperly routing boreholes through rock layers with natural resources,and/or drilling into undesired rock formations in a manner that weakensthe subterranean rock formations and/or diluting target formations withundesired rock formations. Furthermore, oil and/or gas producers do notcurrently account for anisotropy when imaging and/or determining rocklayer boundary locations due to complexities and uncertainties based onthe relationship between the signal velocity, the angle of propagation,the distance to the boundary of the rock layer, and the profile ofanisotropy associated with the rock layer.

The example methods and apparatus described herein may be used tocalculate the shape and/or boundary of a rock layer or a distance from atool to a rock layer boundary by compensating for the anisotropy in therock layer. The example methods and apparatus may be used to compensatefor the anisotropy by analyzing relationships between time periods anddistances between transmitter(s) and receivers and solving for the angleof each signal received at a receiver to determine an effectiveanisotropic signal velocity. In particular, the example methods andapparatus described herein use the calculated anisotropic signalvelocity for the signal received by each receiver and/or sensor todetermine the distance to a portion of the rock layer boundary.

The example methods and apparatus also include one or more transmitterswithin the tool that includes the receivers. Because the transmitter(s)and receivers are included inline within the same tool, the relationshipbetween the tool and the distance to a rock layer boundary can bedetermined using the signal propagation time, the distance between thetransmitter(s) and receivers, and the signal velocities. Equation 1below shows the relationship between the time for a receiver to receivethe reflected signal (i.e., T), the distance from the receiver to atransmitter that transmitted the signal (i.e., a), the anisotropicsignal velocity (i.e., V₀), and the distance from the tool to theboundary (i.e., X), for a boundary parallel to the wellbore.

$\begin{matrix}{T = \frac{\sqrt{( {2\; X} )^{2} + a^{2}}}{V_{\theta}}} & {{Equation}\mspace{14mu} 1}\end{matrix}$

Equation 1 indicates that the greater a time period, (T) for a signal toreach a receiver, the greater the distance (X) between the boundary andthe tool based on a constant signal velocity (V_(θ)) and distance of areceiver to the transmitter (2 a). The signal takes a longer time periodto be received by receivers farther from the transmitter. This longertime period indicates a lower angle of propagation of the signal withthe boundary and a longer distance for the signal to travel to thereceiver. In a particular example corresponding to the signal 6 of FIG.2 having an angle of propagation θ, the effective signal velocity (i.e.,V_(θ)) may be expressed as shown in Equation 2 below.

$\begin{matrix}{V_{\theta} = \frac{V_{INL}( {1 - ɛ^{2}} )}{1 + {ɛ\; \cos \; \theta}}} & {{Equation}\mspace{14mu} 2}\end{matrix}$

In Equation 2, ε is the difference between the inline velocity (e.g.,V_(INL)) and a perpendicular velocity (e.g., V_(ORT)), divided by theinline velocity. In other examples, Equation 2 may be expresseddifferently to reflect a different relationship between the signalvelocity (i.e., V_(θ)) and the propagation direction θ. FIG. 2 defines θas an angle of transmission and/or reception of the signal. Further, theinline signal velocity (e.g., V_(INL)) is the velocity of the signalmeasured in the direction of the wellbore or borehole based on a timefor the signal to travel linearly from the transmitter to the receiverswithout reflecting off the boundary.

The inline velocity is known by measuring the time for the signal topropagate linearly from a transmitter to a receiver. By knowing thedistance between each transmitter and receiver, the time for a signal toreach each receiver after reflecting off of a rock layer boundary, andthe effective velocity of the signal related to the angle ofpropagation, the example methods and apparatus may use semblanceprocessing to combine the time-distance anisotropic velocity (TDAV)relationship for each transmitter and receiver to model the distance ofthe boundary as a best-fit model. For example, three transmitters,thirteen receivers, and eight sensors per receiver may yield 312different transmitter and receiver TDAV relationships. From theserelationships, the effective signal velocity dependent upon the angle ofpropagation and the distance to the rock layer boundary are modeledusing a best-fit calculation. Because the distance to the boundary andthe angle of propagation within each TDAV relationship are unknowndependent variables, the boundary distance can be expressed as afunction of the angle of propagation and the effective anisotropicsignal velocity. The best-fit calculation then uses the number ofrelationships and the known inline signal velocity to solve for theeffective signal velocity resulting from the angle of propagation. Uponknowing the effective anisotropic velocity for each relationship, thedistance to each reflection point of the rock layer boundary can becalculated using Equation 1.

In examples where the reflecting formation boundary is not substantiallyparallel to the wellbore, Equation 1 may be modified. For example, ifthere is an angle between the reflecting boundary of a rock layer andthe wellbore axis (e.g., φ), the distance X to the reflecting boundaryin the Equation 1 may be replaced with a different relation (e.g., Xcos(φ)). In this example, the distance X is a distance between atransmitter and a reflecting boundary. Further, the distance between atransmitter and a receiver in Equation 1 may be replaced by a differentrelation (e.g., a+2X sin(φ)). With these different example relations,the relationship between the distance to a rock layer boundary, thedistance from a transmitter to a receiver, and the propagation angleremains the same. However, the transmission and/or the reception angle(e.g., θ) may differ by twice the angle between the reflecting boundaryand the wellbore axis (e.g., by 2φ). Even in a homogeneous anisotropicformation the transmitted and the received signal may propagate at twodifferent velocities. The effective velocity may be a weighted averageof these two different velocities. Nevertheless, the effective velocityprovides information about the propagation velocities perpendicular tothe wellbore, information that may not be available by any other means.Additionally, the angle φ between the formation boundary and wellboreaxis may be included in parameters determined by a best-fit procedure.

While the example methods and apparatus described herein provide animaging tool that may include one or more transmitters and/or two ormore receivers, the example methods and apparatus may include an imagingtool having any number of transmitters and/or receivers. For example, asonic and/or seismic imaging tool may include one transmitter and tworeceivers, with each receiver including a sensor. Alternatively, a sonicand/or seismic imaging tool may include three transmitters and thirteenreceivers, with each receiver including eight sensors

FIG. 3 shows a wellsite system 7 in which the example methods andapparatus may be implemented. The wellsite system 7 may be onshore oroffshore. In the example wellsite system of FIG. 3, a borehole 11 isformed in one or more subsurface formations by rotary and/or directionaldrilling. A drillstring 12 is suspended within the borehole 11 and has abottomhole assembly 100 that includes a drill bit 105 at its lower end.The wellsite system 7 includes a platform and derrick assembly 10positioned over the borehole 11 at the surface. The derrick assembly 10includes a rotary table 16, which may engage a kelly 17 at an upper endof the drillstring 12 to impart rotation to the drillstring 12. Therotary table 16 may be energized by a device or system not shown. Theexample drillstring 12 is suspended from a hook 18 that is attached to atraveling block (not shown). Additionally, the drillstring 12 ispositioned through the kelly 17 and the rotary swivel 19, which permitsrotation of the drillstring 12 relative to the hook 18. Additionally oralternatively, a top drive system (not shown) could be used to impartrotation to the drillstring 12.

In the example depicted in FIG. 3, the wellsite system 7 furtherincludes drilling fluid 26. For example, the drilling fluid 26 maycomprise a water-based mud, an oil-based mud, a gaseous drilling fluid,water, gas or other fluid for maintaining bore pressure and/or removingcuttings from the area surrounding the drill bit 105. The drilling fluid26 may be stored in a pit 27 formed at the wellsite. A pump 29 deliversthe drilling fluid 26 to the interior of the drillstring 12 via a portin the rotary swivel 19, causing the drilling fluid 26 to flowdownwardly through the drillstring 12 as indicated by directional arrow8. The drilling fluid 26 exits the drillstring 12 via ports in the drillbit 105 and then circulates upwardly through the annulus region betweenthe outside of the drillstring 12 and the wall of the borehole 11 asindicated by directional arrows 9. The drilling fluid 26 lubricates thedrill bit 105, carries cuttings from the formation up to the surface asit is returned to the pit 27 for recirculation, and creates a mudcakelayer (not shown) (e.g., filter cake) on the walls of the borehole 11.

Additionally, the wellsite system includes a communications relay 45 anda logging and control processor 50. The example communications relay 45may receive information and/or data from sensors, transmitters, and/orreceivers located within the bottomhole assembly 100. The informationmay be received by the communications relay 45 via a wired communicationpath through the drillstring 12 and/or via a wireless communicationpath. The communications relay 45 transmits the received informationand/or data to the logging and control processor 50. Additionally, thecommunications relay 45 may receive data and/or information from thelogging and control processor 50. Upon receiving the data and/orinformation, the communications relay 45 may forward the data and/orinformation to the appropriate sensor(s), transmitter(s), and/orreceiver(s) within the bottomhole assembly 100.

The example logging and control processor 50 may include a userinterface that enables parameters to be input and/or outputs to bedisplayed. Additionally, the logging and control processor 50 maycontrol imaging of a boundary of a rock layer. For example, the loggingand control processor 50 may position the bottomhole assembly 100 and/ora sonic and/or seismic imaging tool within the borehole 11, instructtransmitters to transmit a signal for receivers and/or sensors toreceive.

Additionally, the logging and control processor 50 may calculate adistance from the borehole 11 to a portion of a rock boundary based onthe transmitted and received signal. Furthermore, the logging andcontrol processor 50 may compensate for anisotropy within the rock layerwhile calculating the distance from the borehole 11 to a boundary of therock layer. While the logging and control processor 50 is depicteduphole at the surface and within the wellsite system 7, a portion or theentire logging and control processor 50 may be positioned in thebottomhole assembly 100 and/or in a remote location. The logging andcontrol processor 50 is described in greater detail in conjunction withFIG. 6.

In some examples, the tools of the bottomhole assembly 100 of FIG. 3 mayinclude any number and/or type(s) of logging-while-drilling (LWD)modules or tools (two of which are designated by reference numerals 120and 120A) that may be housed in respective drill collars. The LWDmodules 120 and/or 120A may be part of an LWD tool suite of the typedisclosed in P. Breton et al., “Well Positioned Seismic Measurements,”Oilfield Review, pp. 32-45, Spring 2002, incorporated herein byreference. The bottomhole assembly 100 may also includemeasuring-while-drilling (MWD) modules (one of which is designated byreference numeral 130), and a rotary-steerable system or mud motor 150.The MWD module 130 may measure the azimuth and inclination of the drillbit 105 to, for example, monitor the borehole trajectory.

The bottomhole assembly 100 includes capabilities for measuring,processing and/or storing information, as well as for communicatinginformation via, for example, a transmitter 122 and/or receivers 132A-B.The transmitter 122 is shown within the LWD module 120. However, thetransmitted 122 may be included within the MWD module 130 and/or withina separate sonic and/or seismic imaging tool. Additionally, thereceivers 132A-B are shown within the MWD module 130. However, thereceivers 132A-B may be included within the LWD module 120 and/or withina separate sonic and/or seismic imaging tool. The transmitter 122 and/orthe receivers 132A-B may be communicatively coupled to thecommunications relay 45 and/or the logging and control processor 50.Furthermore, although the single transmitter 122 is shown, otherexamples may include two or more transmitters. Additionally, althoughonly the two receivers 132A-B are shown, other examples may include moreor fewer receivers.

The transmitter 122 may be capable of transmitting any signal including,but not limited to, acoustic signals, seismic signals, sonic signals,ultrasonic signals, and/or any other compression and/or shear signals.The receivers 132A-B may include sensors that are capable of receivingthe signal type generated by the transmitter. For example, if thetransmitter 122 generates a seismic or acoustic signal with a centerfrequency of 8 kHz, sensors within the receivers 132A-B may beconfigured to detect the seismic signal with a 8 kHz center frequencywhile filtering other signals types. The transmitter 122 may include anytype of device capable of generating a signal, while the receivers132A-B include sensors that are configured to detect and transduce asignal into electrical data for processing by the logging and controlprocessor 50.

Although the components of FIG. 3 are shown and described as beingimplemented in a particular conveyance type, the example methods andapparatus described herein are not limited to a particular conveyancetype but, instead, may be implemented in connection with differentconveyance types including, for example, coiled tubing, wireline, wireddrill pipe, and/or any other conveyance types known in the industry.Additionally or alternatively, the examples described herein may beimplemented with smart wells and/or intelligent completions.

FIG. 4 shows an example offshore rig 410 that includes alogging-while-drilling (LWD) tool 430. The offshore rig 410 includes thetransmitter 122 of FIG. 3 deployed near the surface of the water.Alternatively, the transmitter 122 may be deployed within the LWD tool430. Additionally, the offshore rig 410 may include a processor tocontrol the transmission of signals from the transmitter 122. Theoffshore rig 410 may also include acoustic receivers and/or a recorderto capture reference signals near the transmitter 122. Furthermore, theoffshore rig 410 may include telemetry equipment for receiving signalsfrom the transmitter 122 and/or the receivers 132A-B within the LWD 430.

The telemetry equipment and/or the recorder may be coupled to aprocessor so that transmitted and received signals may be synchronizedusing uphole and downhole clocks. The example LWD tool 430 may besimilar to the LWD modules 120 and/or 120A of FIG. 3 described in U.S.Pat. No. 6,308,137, incorporated herein by reference. The LWD tool 430includes at least the receivers 132A-B, which may be communicativelycoupled to a signal processor so that recordings may be made of signalsdetected by the by the receivers 132A-B in synchronization with thetransmitting of the signals by the transmitter 122.

FIG. 5 shows an example seismic imaging tool 502 within a subterraneanformation 500 having a first rock layer 504 and a second rock layer 506forming a boundary 507 with the first rock layer 504. The exampleseismic imaging tool 502 is located inline within a borehole 508 and ispositioned parallel to the boundary of the first rock layer 504 to beimaged. The seismic imaging tool 502 may be used to image a shape and/orthe boundary of the first rock layer 504 such as where the first rocklayer 504 meets the second rock layer 506 at the boundary 507.Additionally, it should be recognized that the seismic imaging tool 502may not be shown to scale in relation to the borehole 508 and/or therock layers 504 and 506.

The example of FIG. 5 includes the two adjacent rock layers 504 and 506that may include any types of subterranean rock. Furthermore, the rocklayers 504 and 506 may include the same general rock type but the firstrock layer 504 may include a rock type with a first type ofdirectionally aligned sediment while the second rock layer 506 includessediment aligned in a different direction. Alternatively, the rocklayers 504 and 506 may include similar types of rocks with differentdirections of stress and/or fracturing.

The seismic imaging tool 502 may be included within the bottomholeassembly 100 of FIG. 3 or, alternatively, may be a separate imagingtool. A control device (not shown) may be structurally coupled to theseismic imaging tool 502 to position and/or move the tool 502 within theborehole 508. Additionally, the seismic imaging tool 502 may becommunicatively coupled to the logging and control processor 50 of FIG.3.

The example seismic imaging tool 502 includes transmitters 122A-B, whichare similar or identical to the transmitter 122 of FIG. 3. Furthermore,the seismic imaging tool 502 includes receivers 132A-D that are similaror identical to the receivers 132A-B of FIG. 3. The transmitters 122A-Bare positioned some distance away from the receivers 132A-D.Additionally, each of the receivers 132A-D is spaced apart from theother receivers 132A-D. Moreover, each of the receivers 132A-D mayinclude one or more sensors circumferentially positioned around theexterior of the receiver. For example, if the seismic imaging tool 502is cylindrical in shape, a receiver with eight sensors may have sensorspositioned every 45 degrees around the circumference of the receiver.Likewise, if the seismic imaging tool is rectangular in shape, twosensors may be positioned on each side of the receiver.

The example of FIG. 5 shows the transmitter 122A transmitting a signal510 through the first rock layer 504. The signal 510 is depicted asthree wavefronts. The signal 510 may include any type of transmittablesignal including an acoustic signal, a seismic signal, a sonic signal,an ultrasonic signal, and/or any other suitable signal. The frequency,amplitude, and/or power may be specified such that the signal 510propagates through the first rock layer 504 and reflects off theboundary 507 between the first rock layer 504 and the second rock layer506.

The example signal 510 is transmitted by the transmitter 122A as a wavein all directions (i.e., omnidirectionally). Thus, as each portion ofthe signal propagates through the rock layer 504 and reflects off theboundary 507 with the second rock layer 506, the receivers 132A-Dreceive respective reflected portions of the signal 510. In this manner,the receivers 132A-D may each receive a reflected portion of thetransmitted signal 510. FIG. 5 shows the signal 510 affected byanisotropy within the first rock layer 504. For example, the signal 510is shown as propagating faster in the inline direction (e.g., V_(INL))compared to the signal 510 propagating in the orthogonal direction(e.g., V_(ORT)). In other examples, the signal 510 may propagate throughthe first rock layer 504 faster in the orthogonal direction than theinline direction.

FIG. 6 shows the seismic imaging tool 502 transmitting and receivingsignals affected by anisotropy within the first rock layer 504 of FIG.5. In FIG. 6, the first rock layer 504 is transparent for clarity ofexplanation. The subterranean rock formation 500 of FIG. 6 includes theseismic imaging tool 502 with the transmitters 122A-B and the receivers132A-D of FIG. 5. Additionally, the example signal 510 of FIG. 5 isshown in FIG. 6 as signal paths 602-608.

The signal paths 602-608 originate at the transmitter 122A. The firstsignal path 602 is received by the first receiver 132A and is reflectedby the boundary 507 at a first reflection point 612 at a reflectionangle 610. The second signal path 604 is received by the second receiver132B and is reflected by the boundary 507 of the first rock layer 504 ata second reflection point 614. Similarly, the third signal path 606 isreceived by the third receiver 132C and is reflected by the boundary 507of the first rock layer 504 at a third reflection point 616.Additionally, the fourth signal path 608 is received by the fourthreceiver 132D and is reflected by the boundary 507 of the first rocklayer 504 at a fourth reflection point 618. Furthermore, thetransmission angles with respect to an axis orthogonal to the boundary507 of each of the signal paths 602-608 through the first rock layer 504are the same as the reflection angles (e.g., the reflection angle 610)at the respective reflection points 612-618.

Because the distance from the reflection points 612-618 to therespective receivers 132A-D is relatively short, the boundary 507 of thefirst rock layer 504 may be modeled as a flat or planar surface at aconstant distance from the tool 502 despite the fact that rock layerboundaries are typically at least somewhat uneven. The small signalreception area of the receivers 132A-D receives only a small portion ofthe signal 510 that is reflected from a small scale reflection point atthe boundary 507. For example, the small scale reflection point may onlybe a few decimeters (dm) from the tool 502. At this small scale, areflection point (e.g., each of the reflection points 612-618) may bemodeled as a substantially flat or planar surface. In examples where thefirst rock layer boundary 507 is slanted, curved, or otherwise definedas a surface that is not at a substantially constant distance from thetool 502, seismic image processing may still model the small scalenature of the portion of the boundary as a flat or planar surface. Then,signal migration of multiple seismic images from different portions ofthe boundary 507 may be used to combine the calculated distances fromthe tool 502 to the boundary into a smooth continuous boundary tocompensate for the localized flat surfaces provided by the seismicimaging processing.

The reflection points 612-618 are generally mid-points of the respectivesignal paths 602-608. Additionally, the distance between thetransmitters 122A-B and the receivers 132A-D is known based onspecifications of the seismic imaging tool 502. As a result of the knowndistances, a distance 620 between the tool 502 and the boundary 507 ofthe first rock layer 504 can be calculated based on the time requiredfor each of the signal paths 602-608 to propagate from the firsttransmitter 122A to the respective receivers 132A-D. Additionally, aninline velocity can be calculated when an inline portion of the signal510 is received by any one of the receivers 132A-D. This inline portionof the signal 510 propagates directly within the first rock layer 504from the transmitter 122A in a direction parallel to (.e., along thelongitudinal axis of) the seismic imagining tool 502 to the receivers132A-D.

The signal velocity associated with each of the signal paths 602-608 isaffected by the anisotropy within the first rock layer 504. In theexample of FIG. 6, signal portions traveling at an angle that is closerto in the inline direction propagate faster due to the anisotropy. Forexample, the portion of the signal 510 associated with the signal path608 may have a greater velocity than portions of the signal 510associated with the signal paths 602-606. Similarly, the signal portionassociated with the signal path 606 may have a greater velocity than thesignal portions associated with the signal paths 602-604. As a result ofthe signal portions having different velocities, the propagation timeperiods for each of the signal portions along the respective signalpaths 602-608 are based not only on the distance traveled by the signalportions along the signal paths 602-608 but also on the anisotropicvelocity of each of the signal portions.

In calculating the distance 620, the effect of anisotropy in the firstrock layer 504 can be compensated by relating the anisotropic signalvelocity of each of the signal paths 602-608, the angles of reflectionfor each signal paths 602-608, the known distances between thetransmitters 122A-B and the receivers 132A-D, the inline signalvelocity, and the time period or the transmission time for each of thesignal paths 602-608. In addition to the signal paths 602-608 shown inFIG. 6, additional signal paths may be associated with each of thesensors positioned around the receivers 132A-D. Furthermore, the secondtransmitter 122B may transmit a second signal to be received by each ofthe receivers 132A-D. Still further, the example in FIG. 6 may includeadditional receivers and/or transmitters (not shown).

The logging and control processor 50 of FIG. 3 may compile the collectedtransmission time periods for each of the signal paths 602-608 as wellas the transmission time periods for any other signal paths not shown.The logging and control processor 50 may then model the combined datainto a best-fit model (e.g., a linear programming model) that determinesthe distance 620. Additionally, the model may determine a distance fromeach of the transmitters 122A-B and/or receivers 132A-D to the boundary507 of the first rock layer 504.

Furthermore, signal migration may be implemented to determine thedistance of the boundary of the first rock layer 504 from the tool 502at the reflection points 612-618 and any other reflection points notshown. These distances may then be modeled to generate an image of aportion of the boundary 507 of the first rock layer 504. Upon imagingthis portion of the first rock layer boundary 504, the seismic imagingtool 502 may be moved a distance (e.g., 6 inches) to determine adistance to the next portion of the first rock layer boundary 504.

FIG. 7 shows an example functional diagram of the logging and controlprocessor 50 of FIG. 3. The example logging and control processor 50sends transmission instructions to a tool (e.g., the example tool 502,the LWD modules 120 and 120A, and/or the MWD module 130) and processesreceived signals and/or messages from the tool to calculate a distancefrom the tool to a portion of a rock layer boundary using anisotropiccompensation of the signal velocity. Additionally, the logging andcontrol processor 50 may use signal migration and/or semblanceprocessing of multiple portions of calculated boundary positions toimage and/or determine a continuous rock layer boundary.

To receive signals and/or messages from sensors and/or receivers withinthe tool, the example logging and control processor 50 includes an inputreceiver 702. The example input receiver 702 receives the signals and/ormessages via a communication path 720 that may be communicativelycoupled to the tool that includes the transmitters, receivers, and/orsensors. The communication path 720 may include any wired communicationpath(s) and/or any wireless communication path(s).

The input receiver 702 may receive the signals and/or messages bypolling each of the receivers and/or sensors for any received signaldata that may have been accumulated or collected by the receivers and/orsensors. Alternatively, the input receiver 702 may receive the signalsand/or messages or, generally, information or data from the sensorsand/or the receivers upon those sensors and/or receivers detecting asignal portion (e.g., a portion of the signal 510 of FIG. 5). Uponreceiving the signals and/or messages, the example input receiver 702may queue the information or data associated with the signals and/ormessages until a formation processor 704 is available to process theinformation. Alternatively, the input receiver 702 may parse thereceived messages for information included within the message includingthe identity of the receiver and/or sensor that detected the signalportion and transmitted the message, the time a signal was detectedand/or any other data included within the signal that was detected. Uponparsing this information, the input receiver 702 may forward the parsedinformation to the formation processor 704 for processing. In yetanother example, the input processor 702 may buffer the receivedmessages until the input processor 702 receives a request for data fromthe formation processor 704. Upon receiving the request, the inputreceiver 702 may forward the data or information included within thereceived signals and/or messages and/or the received messages to theformation processor 704.

To calculate a distance of a subterranean rock layer boundary from atool by compensating for anisotropy within the rock layer, the examplelogging and control processor 50 of FIG. 7 includes the formationprocessor 704. The example formation processor 704 receives messagesand/or data included within the received signals and/or messages fromthe input receiver 702. The example formation processor 704 then matchesthose messages and/or data with the data associated with thetransmission of the corresponding signal. The data associated withtransmitting the signal may include a time the signal was transmittedfrom a transmitter (e.g., a timestamp), the signal type, and/or anyother data included within the signal.

By matching the received messages to the transmitted signals and/ormessage data, the formation processor 704 can calculate the inlinevelocity of the signal and determine the time period elapsed for eachsignal portion to propagate from the transmitter to the correspondingsensor and/or receiver. The formation processor 704 calculates thepropagation time by subtracting the time at which a portion of thesignal was received by a sensor and/or receiver from the time at whichthe signal was transmitted. Additionally, the example formationprocessor 704 may calculate the inline signal velocity by determining afirst instance or occurrence for a received signal and/or message from areceiver, calculating the time period for the signal to propagate fromthe transmitter to the receiver and/or sensor, and dividing the distancebetween the transmitter and the receiver by the time period. Further,the example formation processor 704 may calculate the inline signalvelocity by using semblance analysis of the signal traveling alongreceivers within the seismic and/or sonic tool.

The first instance of the received signal and/or message is generally aportion of the signal traveling in the direction along the tool (i.e.,inline) because this is the shortest distance for the signal to travel.Subsequent instances or occurrences of the receiver receiving portionsof the signal are generally from reflections off the rock layer boundary507 because the distance to the rock layer boundary 507 and back to thetool is greater than the distance directly from the transmitter to thereceiver.

The example formation processor 704 may determine distances between eachtransmitter and receiver and/or sensor by accessing a tool propertydatabase 706. For example, if the formation processor 704 processes areceived signal or message that indicates the signal portion wasreceived by a sensor with an identification value of DM01, the formationprocessor 704 may access the database 706 to determine that the sensorDM01 has a location that is two meters from the transmitter.

Upon calculating the time periods, the example formation processor 704may generate an equation (e.g., using Equations 1 and/or 2 above), amathematical relationship, and/or the time-distance anisotropic velocityrelationships for each receiver and/or sensor that relates a distance toa portion of a rock layer boundary to a propagation time of the signal,a distance of the receiver from the transmitter, the inline velocity ofthe signal, and/or the anisotropic velocity of the signal portionreceived.

Additionally, the formation processor 704 may determine an orthogonalsignal velocity based on a distance to a portion of a rock layerboundary, a propagation time of the signal, a distance of the receiverfrom the transmitter, and/or the inline velocity of the signal. Theformation processor 704 may then combine the equations into anexpression and/or data model (e.g., a system or matrix of equations) todetermine the anisotropic velocity of each signal portion and/or adistance to a portion of the rock layer boundary. The anisotropicvelocity of each signal portion may be expressed as a ratio of theinline velocity and an angle of propagation and/or reflection of thesignal portion through the rock layer (e.g., using Equation 2 above).

The example formation processor 704 may determine that additional datais needed to calculate a distance to a boundary. In these cases, theformation processor 704 may send a message to a command processor 706 toinstruct a transmitter to transmit another signal. Upon receiving thismessage, the command processor 706 may instruct a transmission manager708 to instruct a transmitter to transmit a signal. The instructions mayinclude a time to transmit the signal and/or a signal type (e.g., signalfrequency, signal amplitude, signal duration, etc.).

The formation processor 704 may utilize a plurality of equations todetermine the angle of propagation for each signal portion to determinethe anisotropic velocity and the distance to a portion of the rock layerboundary. Because the angle of propagation is dependent on the distanceto the boundary 507 (FIG. 5), the formation processor 704 may utilizeany best fit model, least squares best fit model, a varianceminimization best fit model, and/or any other best fit model.Alternatively, the formation processor 704 may organize the equationsinto a matrix or system of equations to model and/or determine thedistance to the rock layer boundary. Furthermore, because the points ofreflection of the signal portions are some distance apart, the formationprocessor 704 may determine a distance from each point of reflection atthe boundary 507 to an orthogonal point in the tool.

Upon calculating the distance(s) from the tool to the portion of therock layer boundary being imaged or measured, the formation processor704 forwards these distance(s) to a boundary migrator 710. The exampleboundary migrator 710 determines distances between the calculateddistances between the tool and the rock layer boundary 507 to generate acontinuous rock layer boundary for imaging. For example, if the boundarymigrator 710 receives the distance to reflection points 612 and 614 ofFIG. 6 from the formation processor 704, the boundary migrator 710determines the distances from between the points 612 and 614 to the tool502. The example boundary migrator 710 determines these distances usingmigration processing that estimates the distances to the boundary 507between the points 612 and 614 based on the measured or calculateddistances associated with the points 612-618.

Additionally, the example boundary migrator 710 of FIG. 7 may store thecalculated distances to a database. Then, as the tool moves within theborehole to determine distances to (i.e., to image) other portions ofthe boundary, the boundary migrator 710 migrates (e.g., interpolates)the distances to the rock layer boundary between the measurementlocations of the tool. For example, if there is a seven foot spacingbetween measurement locations of the tool, the boundary migrator 710 mayestimate the rock layer boundary between these points based on thecalculated distances. As a result of the migration processing, theboundary migrator 710 generates a continuous subterranean rock layerboundary for portions of the rock layer that have been measured.

The example boundary migrator 710 may also create images from thecalculated and/or estimated distances of the rock layer boundary. Theseimages may show the rock layer shape, depth, boundary and/or any otherinformation that may be determined from the calculated distances. Theexample boundary migrator 710 may transmit the images, the calculateddistances and/or the estimated distances to an operator via acommunication path 728.

The example logging and control processor 50 includes the commandprocessor 706 to manage the activities and/or functions of the formationprocessor 704, the boundary migrator 710, and/or the transmissionmanager 708. The command processor 706 may receive commands from an oiland/or gas producer operator via a communication path 726. The operatormay send instructions to the command processor 706 to initiate imagingof a rock layer boundary, to initiate image processing of a rock layerboundary, and/or to determine an operating efficiency of the formationprocessor 704. Additionally, an operator may transmit an image profileto the example command processor 706 to specify locations within aborehole that a tool is to image and/or measure. The command processor706 may then manage the timing of the transmission of signals and theprocessing of the received data via the formation processor 704 toensure a rock layer is measured and/or imaged according to the imageprofile. Additionally, the command processor 706 may instruct themovement of the tool.

To manage the generation and transmission of commands to transmitters,sensors, and/or receivers included within the tool, the example loggingand control processor 50 of FIG. 7 includes the transmission manager708. Upon receiving an instruction to transmit a signal, thetransmission manager 708 determines which transmitter is to transmit thesignal, a time at which the signal is to be transmitted, the type ofsignal to be transmitted, and/or any signal properties of the signal tobe transmitted. The example transmission manager 708 then sends atransmission message to the corresponding transmitter included withinthe tool via a communication path 722. The communication path 722 mayinclude any wired and/or wireless communication path(s).

The transmission message may include the signal type the transmitter isto transmit, a duration for the transmission of the signal (e.g., 1second), a time at which the signal is to be transmitted, and/or signalproperties (e.g., amplitude, frequency, etc.). Alternatively, thetransmission manager 708 may send a transmission message to theappropriate transmitter at the time the transmitter is to transmit asignal. Upon receiving the message, the transmitter may then transmitthe specified signal. Additionally, the transmission manager 708 maysend a transmission message to the receivers and/or sensors to alert thereceivers and/or sensors that a signal will be transmitted. This alertmay activate the sensors and/or receivers and/or may provide to thesensors and/or receivers the time at which the signal will betransmitted.

The example tool property database 706 stores known properties of thetool, including distances between transmitters, receivers and/or sensorsand/or locations of the sensors around a circumference of the tool. Thedatabase 706 may also store the angle of orientation for each of thesensors and/or the signal type(s) that the transmitters are configuredto output. Furthermore, the database 706 may store identificationinformation for each of the transmitters, receivers, and/or sensors. Thedata within the database 706 may be updated, added to, deleted, and/ormodified by an operator via a communication path 724. For example, anoperator may modify distances between receives and transmitters after aredesign of the tool. The tool property database 706 may be implementedby random access memory (RAM), read-only memory (ROM), a programmableROM (PROM), an electronically-programmable ROM (EPROM), anelectronically-erasable PROM (EEPROM), and/or any other type of memory.

While an example manner of implementing the logging and controlprocessor 50 is depicted in FIG. 7, one or more of the interfaces, datastructures, elements, processes and/or devices illustrated in FIG. 7 maybe combined, divided, rearranged, omitted, eliminated and/or implementedin any other way. For example, the example input receiver 702, theexample formation processor 704, the example command processor 706, theexample transmission manager 708, and/or the example boundary migrator710 illustrated in FIG. 7 may be implemented separately and/or in anycombination using, for example, machine-accessible or readableinstructions executed by one or more computing devices and/or computingplatforms (e.g., the example computing system 1100 of FIG. 11).

Further, the example input receiver 702, the example formation processor704, the example command processor 706, the example transmission manager708, the example boundary migrator 710 and/or, more generally, theexample logging and control processor 50 may be implemented by hardware,software, firmware and/or any combination of hardware, software and/orfirmware. Thus, for example, any of the example input receiver 702, theexample formation processor 704, the example command processor 706, theexample transmission manager 708, the example boundary migrator 710and/or, more generally, the example logging and control processor 50 canbe implemented by one or more circuit(s), programmable processor(s),application specific integrated circuit(s) (ASIC(s)), programmable logicdevice(s) (PLD(s)) and/or field programmable logic device(s) (FPLD(s)),etc.

FIGS. 8, 9, and 10 are flowcharts depicting example processes that maybe carried out to implement the example logging and control processor50, the example seismic imaging tool 502, the example transmitters122A-B, the example receivers 132A-D, the example formation processor704, the example boundary migrator 710, the example command processor706, and/or the transmission manager 708 of FIGS. 3, 5, 6, and/or 7. Theexample processes of FIGS. 8, 9, and/or 10 may be carried out by aprocessor, a controller and/or any other suitable processing device. Forexample, the example processes of FIGS. 8, 9, and/or 10 may be embodiedin coded instructions stored on any tangible computer-readable mediumsuch as a flash memory, a CD, a DVD, a floppy disk, a ROM, a RAM, aprogrammable ROM (PROM), an electronically-programmable ROM (EPROM), anelectronically-erasable PROM (EEPROM), an optical storage disk, anoptical storage device, magnetic storage disk, a magnetic storagedevice, and/or any other medium that can be used to carry or storeprogram code and/or instructions in the form of methods, processes ordata structures, and which can be accessed by a processor, ageneral-purpose or special-purpose computer, or other machine with aprocessor (e.g., the example computing system 1100 discussed below inconnection with FIG. 11). Combinations of the above are also includedwithin the scope of computer-readable media.

Processes comprise, for example, instructions and/or data that cause aprocessor, a general-purpose computer, special-purpose computer, or aspecial-purpose processing machine to implement one or more particularprocesses. Alternatively, some or all of the example operations of FIGS.8, 9, and/or 10 may be implemented using any combination(s) of ASIC(s),PLD(s), FPLD(s), discrete logic, hardware, firmware, etc.

Also, one or more of the example operations of FIGS. 8, 9, and/or 10 maybe implemented using manual operations or as any combination of any ofthe foregoing techniques, for example, any combination of firmware,software, discrete logic and/or hardware. Further, other processesimplementing the example operations of FIGS. 8, 9, and/or 10 may beemployed. For example, the order of execution of the blocks may bechanged, and/or one or more of the blocks described may be changed,eliminated, sub-divided, or combined. Additionally, any or all of theexample operations of FIGS. 8, 9, and/or 10 may be carried outsequentially and/or carried out in parallel by, for example, separateprocessing threads, processors, devices, discrete logic, circuits, etc.

The example process 800 of FIG. 8 determines known parameters associatedwith transmitters and/or receivers included within a seismic imagingtool (e.g., the seismic imaging tool 502), a LWD module, a MWD module,and/or any other type of measuring device that includes transmittersand/or receivers. By determining the known parameters including thenumber of transmitters, receivers, and/or sensors, these knownparameters associated with a tool may be accessed by the exampleformation processor 704 of FIG. 7 to calculate and/or model a distanceof the tool from a rock layer boundary using anisotropy compensation.The example process 800 may be executed upon the setup and/or prior tolowering the seismic imaging tool, LWD module, and/or MWD module into aborehole. Additionally, the example process 800 may be carried out uponthe specification and/or design of the seismic imaging tool, LWD module,and/or MWD module.

The example process 800 begins by identifying and storing the number oftransmitters included within the seismic imaging tool, LWD module,and/or MWD module (block 802). Next, the example process 800 identifiesand stores the number of receivers within the seismic imaging tool, LWDmodule, and/or MWD module (block 804). The example process 800 thenidentifies and stores the number of sensors per receiver and theposition of each sensor on the respective receivers (blocks 806 and808). The position of a sensor may be identified by indicating on whichside of a tool the sensor is located and/or whether the sensor isdirectionally positioned to receive signals from downhole, uphole,orthogonal to the tool, or at an angle to the tool.

The example process 800 continues by identifying and storing a distancebetween each transmitter and each receiver (block 810). The distancesmay be calculated from the closet point of the transmitter to a closestpoint on the receiver or a midpoint of the transmitter to a midpoint ofthe receiver. Alternatively, the example process 800 may includecalculating a distance from each transmitter to each sensor within eachreceiver. The example process 800 then identifies and stores the signaltype to be emitted by the transmitter(s) (block 812). The signal typemay include a frequency of the signal, an amplitude of the signal,and/or any other signal properties. Alternatively, the command processor706 of FIG. 7 may select a signal type to transmit if the transmittersare capable of transmitting more than one type of signal. Upon selectinga signal type to transmit, the command processor 706 may transmit thesignal type to the formation processor 704 to calculate and model adistance to a rock layer boundary. The number of transmitters,receivers, sensors per receiver, distance and/or signal type identifiedby the example process 800 may be stored to the tool property database706 of FIG. 7. Additionally, identifying the sensors, transmittersand/or receivers may include storing a unique identification valueassociated with each device. An identification value may be includedwithin any message transmitted by the transmitters, the receivers,and/or the sensors. Upon identifying the signal type, the exampleprocess 800 ends.

The example process 900 of FIG. 9 determines a distance between a tooland a rock layer boundary by compensating for anisotropy within the rocklayer. Multiple example processes 900 may be executed in parallel orseries as multiple signals are transmitted by transmitter(s) within atool. Additionally, multiple example processes 900 may be executed inparallel or series as multiple signals are transmitted by transmitter(s)within other tools communicatively coupled to a common processor (e.g.,the example logging and control processor 50 of FIG. 7).

The example process 900 begins by transmitting a first signal from afirst transmitter within a seismic imaging tool, LWD module, and/or MWDmodule (block 902). The first signal is transmitted through asubterranean rock layer. A portion of the first signal may reflect off aboundary of the subterranean rock layer back to one or more receivers.Additionally, another portion of the first signal may travel inline withthe tool and be received by one or more receivers to determine an inlinevelocity of the first signal. After a time period, the first signal isreceived by a receiver (block 904). The first signal may be received byone or more sensors within the receiver. Next, the receiver identifiesthe sensor(s) that received a portion of the first signal (block 906).The receiver may identify the sensors by a unique identification messagetransmitted from each sensor that received the first signal. Uponidentifying the sensors, the receiver transmits a received signalmessage to the example formation processor 704 within the logging andcontrol processor 50 of FIG. 7 (block 908). The received signal messagemay include a time the signal was received, an identification value ofthe sensor, an identification value of a receiver that received thesignal, and/or any other data that may have been included within thesignal (e.g., an identification value of the transmitter, a time thesignal was transmitted, etc.). Alternatively, each of the sensors maytransmit a received signal message including a unique identifier of thesensor to the logging and control processor 50.

The example process 900 continues by determining if any additionalsensors within other receivers have also received the first signal(block 910). If one or more of the other sensors have received the firstsignal (blocks 910 and 904), those corresponding receivers identify thesensor(s) that received the signal (block 908). The example process 900may determine if there are no other receivers to receive a signal if thelogging and control processor 50 has received signal messages from allthe receivers and/or if after a specified time period, the exampleprocess 900 determines that the signal did not reach a receiver and/or areceiver did not detect a portion of the first signal. This time periodmay be an estimation of the time for the first signal to propagatethrough the first rock layer to reach all of the receivers includedwithin the tool. If no other receiver has received the signal, theexample process 900 determines if another signal is to be transmittedfrom a transmitter (block 912).

If the example process 900 of FIG. 9 determines that another signal isto be transmitted (block 912), the example process 900 instructs atransmitter to transmit another signal (block 914). The transmitter thattransmits the additional signal may include the transmitter thattransmitted the first signal and/or a different transmitter. Upontransmitting another signal, the example process executes blocks 906-910again. However, if the example process 900 of FIG. 9 determines thatanother signal is not to be transmitted (block 912), the example process900 calculates a distance from the tool, the receiver(s), and/or thetransmitter(s) to a portion of a boundary of the rock layer (block 916).The example process 916 in conjunction with FIG. 10 details thecalculation of the distance including compensation for anisotropy withinthe rock layer.

Upon determining and/or modeling the distance to the boundary, theexample process 900 stores the distance (block 918). This distance maybe stored to the example boundary migrator 710 and/or any otherdatabase. Next, the example process 900 determines if the tool is to bemoved to another location within the borehole (block 920). If the toolis to be moved to image another portion of the boundary of the rocklayer, the tool is moved a specified distance and a signal istransmitted from a transmitter (block 914). The specified distance forthe tool to be moved may range from a few centimeters to a fewkilometers depending on the process type to image the complete boundary.

If the tool is not to be moved to another location (block 920), theexample process 900 migrates the calculated distances to determineand/or model the boundary of the subterranean anisotropic rock layer(block 922). Migrating the calculated distances may includeinterpolating the unmeasured portions of the boundary between measuredportions of the boundary to some average of the portions of the boundarywith known calculated distances. Upon determining the boundary of thesubterranean rock layer, the example process 900 ends.

FIG. 10 depicts an example manner of implementing the process 916 ofFIG. 9. The example process 916 of FIG. 10 calculates and/or models adistance between a tool and a rock layer boundary by compensating foranisotropy within the rock layer. Multiple example processes 916 may beexecuted in parallel or series as multiple signals are transmitted bytransmitter(s) within a tool. Additionally, multiple example processes916 may be executed in parallel or series as multiple signals aretransmitted by transmitter(s) within other tools communicatively coupledto a common processor (e.g., the example logging and control processor50 of FIG. 7).

The example process 916 begins by compiling received signals and/ormessages from each receiver and/or sensor for a single location of atool within a borehole (block 1002). Each received signal and/or messagemay include a time the signal or message was received by a receiverand/or sensor, an identification value of the sensor and/or receivedthat received the signal or message, and/or any other data that may havebeen included within the signal or message (e.g., identification valueof the transmitter, time the signal was transmitted, etc.).Additionally, the example process 916 may match the received signal datato data associated with the corresponding transmitted signal.

Next, the example process 916 accesses the tool property database 706 ofFIG. 7 to determine the stored distances between each of thetransmitters, receivers and/or sensors (block 1004). The example process916 then determines the inline signal velocity of the transmitted signal(block 1006). The inline signal velocity may be determined byidentifying a time period corresponding to when one or more receiversand/or sensors detected a first instance of the transmitted signal. Whena signal is transmitted, the first instance of the signal received by asensor should be a portion of the signal propagating in the direction ofthe tool. Portions of the signal that are received at a later timeperiod arrive later because those portions of the signal have a greaterdistance to travel by reflecting off a boundary and returning to thetool. Thus, the example process 916 may identify the first instance ofthe received signal, determine the time period from when the signal wastransmitted to when the signal was received, and divide a distancebetween the transmitter and the receiver and/or sensor that received thesignal by that time period to determine the inline signal velocity.

The example process 916 of FIG. 10 continues by calculating a timeperiod for each portion of the received signal to propagate from thetransmitters to each sensor and/or receiver (block 1008). Then, for eachtransmitter and each sensor and/or receiver, the example process 916generates an equation relating a distance to a portion of a rock layerboundary to the calculated time period, the distance between thereceiver and/or sensor with the transmitter, and/or an anisotropicvelocity of the signal (block 1010). The anisotropic velocity of theportion of the signal received may be expressed as a ratio of the inlinevelocity similar to Equation 2 above.

The example process 916 then compiles the equations for each transmitterand receiver and/or sensor (block 1012). Next, the example process 916combines the compiled equations to solve for the anisotropic signalvelocity for each equation (block 1014). The example process 916 maycombine the equations (e.g., equations similar to Equation 1) into amatrix where the anisotropic velocity of each signal portion is theunknown variable. Alternatively, the anisotropic velocity of each signalportion may be determined by modeling the combined equations todetermine a best fit solution. The example process 916 may then orconcurrently determine the distance to the portion of the subterraneananisotropic rock layer boundary (block 1016). Upon determining theanisotropic velocity for each signal portion, the example process maydetermine the distance using an equation similar to Equation 1.Alternatively, the example process 916 may determine the distance to theboundary by solving for the distance in the same model that alsodetermines the anisotropic signal velocity. In this manner, the best fitmodel solves for the distance while solving for the anisotropic velocityfor each signal. Generally, the larger the number of equations, the moreaccurate the model may be to determine the anisotropic signal velocityand/or a distance to the boundary. For example, a tool with threetransmitters, thirteen receivers, and eight sensors per receiver mayyield 312 equations while one transmitter, two receivers, and twosensors per receiver may yield four equations. Upon determining thedistance to a portion of the rock later boundary, the example process916 ends.

FIG. 11 is a block diagram of an example computing system 1100 that maybe used to implement the example methods and apparatus described herein.For example, the computing system 1100 may be used to implement theexample logging and control processor 50, the example formationprocessor 704, and/or the example boundary migrator 710. The examplecomputing system 1100 may be, for example, a conventional desktoppersonal computer, a notebook computer, a workstation or any othercomputing device. A processor 1102 may be any type of processing unit,such as a microprocessor from the Intel® Pentium® family ofmicroprocessors, the Intel® Itanium® family of microprocessors, theIntel® Core™ family of microprocesors, and/or the Intel XScale® familyof processors. Memories 1106, 1108 and 1110 that are coupled to theprocessor 1102 may be any suitable memory devices and may be sized tofit the storage demands of the system 1100. In particular, the flashmemory 1110 may be a non-volatile memory that is accessed and erased ona block-by-block basis.

An input device 1112 may be implemented using a keyboard, a mouse, atouch screen, a track pad or any other device that enables a user toprovide information to the processor 1102.

A display device 1114 may be, for example, a liquid crystal display(LCD) monitor, a cathode ray tube (CRT) monitor or any other suitabledevice that acts as an interface between the processor 1102 and a user.The display device 1114 as pictured in FIG. 11 includes any additionalhardware required to interface a display screen to the processor 1102.

A mass storage device 1116 may be, for example, a conventional harddrive or any other magnetic or optical media that is readable by theprocessor 1102.

A removable storage device drive 1118 may, for example, be an opticaldrive, such as a compact disk-recordable (CD-R) drive, a compactdisk-rewritable (CD-RW) drive, a digital versatile disk (DVD) drive orany other optical drive. It may alternatively be, for example, amagnetic media drive. A removable storage media 1120 is complimentary tothe removable storage device drive 1118, in as much as the media 1120 isselected to operate with the drive 1118. For example, if the removablestorage device drive 1118 is an optical drive, the removable storagemedia 1120 may be a CD-R disk, a CD-RW disk, a DVD disk or any othersuitable optical disk. On the other hand, if the removable storagedevice drive 1118 is a magnetic media device, the removable storagemedia 1120 may be, for example, a diskette or any other suitablemagnetic storage media.

At least some of the above described example methods and/or apparatusare implemented by one or more software and/or firmware programs runningon a computer processor. However, dedicated hardware implementationsincluding, but not limited to, application specific integrated circuits,programmable logic arrays and other hardware devices can likewise beconstructed to implement some or all of the example methods and/orapparatus described herein, either in whole or in part. Furthermore,alternative software implementations including, but not limited to,distributed processing or component/object distributed processing,parallel processing, or virtual machine processing can also beconstructed to implement the example methods and/or systems describedherein.

It should also be noted that the example software and/or firmwareimplementations described herein are stored on a tangible storagemedium, such as: a magnetic medium (e.g., a magnetic disk or tape); amagneto-optical or optical medium such as an optical disk; or a solidstate medium such as a memory card or other package that houses one ormore read-only (non-volatile) memories, random access memories, or otherre-writable (volatile) memories. Accordingly, the example softwareand/or firmware described herein can be stored on a tangible storagemedium such as those described above or successor storage media.

Although certain example methods, apparatus, and machine-accessiblemedium have been described herein, the scope of coverage of this patentis not limited thereto. On the contrary, this patent covers all methods,apparatus, and machine-accessible medium fairly falling within the scopeof the appended claims either literally or under the doctrine ofequivalents.

1. A method to calculate a distance from a borehole to a boundary of ananisotropic subterranean rock layer, the method comprising: transmittinga first signal from a first transmitter at a first location in aborehole traversing a subterranean formation; receiving the first signalat a first receiver after a first time period at a second location inthe borehole; receiving the first signal at a second receiver after asecond time period at a third location in the borehole; and calculatinga first distance from the first transmitter to a first portion of aboundary of a subterranean rock layer adjacent to the borehole bycompensating for an anisotropy of the subterranean rock layer based onthe first time period and the second time period.
 2. A method as definedin claim 1, wherein the first time period starts when the first signalis transmitted by the first transmitter and stops when the first signalis received by the first receiver and the second time period starts whenthe first signal is transmitted by the first transmitter and stops whenthe first signal is received by the second receiver.
 3. A method asdefined in claim 1, further comprising: transmitting a second signalfrom a second transmitter at a fourth location in the borehole;receiving the second signal at the first receiver after a third timeperiod; receiving the second signal at the second receiver after afourth time period; calculating a second distance from the secondtransmitter to a second portion of the boundary of the subterranean rocklayer adjacent to the borehole by compensating for the anisotropy of thesubterranean rock layer based on the third time period and the fourthtime period; and determining a distance from the first transmitter tobetween the first portion and the second portion of the boundary of thesubterranean rock layer.
 4. A method as defined in claim 1, wherein: afirst velocity of the first signal from the first transmitter to thefirst receiver is a value between an orthogonal velocity perpendicularto the borehole and an inline velocity based on a first angle ofpropagation of the first signal relative to the first portion of theboundary; and a second velocity of the first signal from the firsttransmitter to the second receiver is a value between the orthogonalvelocity and the inline velocity based on a second angle of propagationof the first signal relative to the first portion of the boundary.
 5. Amethod as defined in claim 4, wherein compensating for the anisotropy ofthe subterranean rock layer includes calculating the first distance fromthe first transmitter to the first portion of the boundary based on atleast one of the first velocity, the second velocity, first time period,the second time period, the first location of the first transmitter, thesecond location of the first receiver, the first distance, the seconddistance, or an inline velocity of the first signal along the borehole.6. A method as defined in claim 5, wherein the first portion of theboundary reflects the first signal based on at least one of a change inrock type from the subterranean rock layer to a second subterranean rocklayer, a change in a lithology of the subterranean rock layer, a changein a fault of the subterranean rock layer, or a change in anunconformity within the subterranean rock layer.
 7. A method as definedin claim 3, wherein the first and second signals are at least one ormore acoustic signals, seismic signals, sonic signals or ultrasonicsignals.
 8. A method as defined in claim 3, further comprising: movingat least one of the first transmitter, the first receiver or the secondreceiver a third distance; transmitting a third signal from the firsttransmitter; receiving the third signal at the first receiver after afifth time period; receiving the third signal at the second receiverafter a sixth time period; calculating a fourth distance from the firsttransmitter to a third portion of the boundary of the subterranean rocklayer by compensating for the anisotropy of the subterranean rock layerbased on the fifth time period and the sixth time period; anddetermining the boundary of the subterranean rock layer based on atleast one of the first distance to the first portion of the boundary,the second distance to the second portion of the boundary, or the thirddistance to the third portion of the boundary.
 9. An apparatus tocalculate a distance from a borehole to a boundary of an anisotropicsubterranean rock layer, the apparatus comprising: a first transmitterat a first location to transmit a first signal within a borehole of asubterranean rock layer; a first receiver at a second location in theborehole to receive the first signal after a first time period; a secondreceiver at a third location in the borehole to receive the first signalafter a second time period; and a formation processor to calculate afirst distance from the first transmitter to a first portion of theboundary of the subterranean rock layer by compensating for ananisotropy of the subterranean rock layer based on the first time periodand the second time period.
 10. An apparatus as defined in claim 9,further comprising a second transmitter at a fourth location in theborehole to transmit a second signal within the borehole of thesubterranean rock layer.
 11. An apparatus as defined in claim 10,wherein: the first receiver receives the second signal after a thirdtime period; the second receiver receives the second signal after afourth time period; and the formation processor calculates a seconddistance from the second transmitter to a second portion of the boundaryof the subterranean rock layer adjacent to the borehole by compensatingfor the anisotropy of the subterranean rock layer based on the thirdtime period and the fourth time period.
 12. An apparatus as defined inclaim 11, further comprising a boundary migrator to determine a distancefrom the first transmitter to between the first portion and the secondportion of the boundary of the subterranean rock layer.
 13. An apparatusas defined in claim 11, wherein at least one of the first transmitter,the second transmitter, the formation processor, or the boundarymigrator is located at a surface.
 14. An apparatus as defined in claim9, wherein the formation processor is to: determine a first velocity ofthe first signal from the first transmitter to the first receiver basedon at least one of a value between an orthogonal velocity perpendicularto the borehole and an inline velocity or a first angle of propagationof the first signal relative to the first portion of the boundary; anddetermine a second velocity of the first signal from the firsttransmitter to the second receiver based on at least one of the valuebetween the orthogonal velocity and the inline velocity or a secondangle of propagation of the first signal relative to the first portionof the boundary.
 15. An apparatus as defined in claim 14, wherein theformation processor compensates for the anisotropy of the subterraneanrock layer by calculating the first distance from the first transmitterto the first portion of the boundary based on at least one of the firstvelocity, the second velocity, first time period, the second timeperiod, the first location of the first transmitter, the second locationof the first receiver, the first distance, the second distance, or aninline velocity of the first signal along the borehole.
 16. An apparatusas defined in claim 9, wherein the first receiver and the secondreceiver include one or more sensors positioned to receive signals fromdifferent directions.
 17. An apparatus as defined in claim 16, whereinthe one or more sensors associated with the first receiver arecircumferentially positioned around the first receiver and the one ormore sensors associated with the second receiver are circumferentiallypositioned around the second receiver.
 18. An apparatus as defined inclaim 16, wherein at least one of the first receiver, the secondreceiver, or the first transmitter is coupled to a tool located in theborehole.
 19. An apparatus as defined in claim 11, wherein: at least oneof the first transmitter, the first receiver or the second receiver ismoved a third distance; the first transmitter transmits a third signal;the first receiver receives the third signal after a fifth time period;the second receiver receives the third signal after a sixth time period;the formation processor calculates a fourth distance from the firsttransmitter to a third portion of the boundary of the subterranean rocklayer by compensating for the anisotropy of the subterranean rock layerbased on the fifth time period and the sixth time period; and theboundary migrator determines the boundary of the subterranean rock layerbased on at least one of the first distance to the first portion of theboundary, the second distance to the second portion of the boundary, orthe third distance to the third portion of the boundary.
 20. Anapparatus as defined in claim 9, farther comprising: a third receiver ata fifth location in the borehole to receive the first signal after athird time period; and a fourth receiver at a sixth location in theborehole to receive the first signal after a fourth time period.
 21. Anapparatus as defined in claim 20, wherein the formation processorcalculates the first distance from the first transmitter to the firstportion of the boundary of the subterranean rock layer by compensatingfor the anisotropy of the subterranean rock layer based on the firsttime period, the second time period, the third time period, and thefourth time period.
 22. An apparatus to calculate a distance from aborehole to a boundary of an anisotropic subterranean rock layer, theapparatus comprising a formation processor to calculate a first distancefrom a first transmitter to a first portion of the boundary of asubterranean rock layer by compensating for an anisotropy of thesubterranean rock layer based on a first time period and a second timeperiod corresponding to a first signal.
 23. An apparatus as defined inclaim 22, wherein the formation processor is to: determine a firstvelocity of the first signal from the first transmitter to a firstreceiver based on at least one of a value between an orthogonal velocityperpendicular to the borehole and an inline velocity or a first angle ofpropagation of the first signal relative to the first portion of theboundary; and determine a second velocity of the first signal from thefirst transmitter to a second receiver based on at least one of thevalue between the orthogonal velocity and the inline velocity or asecond angle of propagation of the first signal relative to the firstportion of the boundary.
 24. An apparatus as defined in claim 23,wherein the formation processor compensates for the anisotropy of thesubterranean rock layer by calculating the first distance from the firsttransmitter to the first portion of the boundary based on at least oneof the first velocity, the second velocity, the first time period, thesecond time period, a first location of the first transmitter, a secondlocation of the first receiver, the first distance, or an inlinevelocity of the first signal along the borehole.